Low-density Lipoprotein Cholesterol Reduction Therapies for Secondary Prevention in Patients with Stroke: A Network Meta-analysis

Background Patients with previous strokes are at a higher risk of stroke recurrence. Current guidelines recommend a range of low-density lipoprotein cholesterol (LDL-C)-lowering treatments to reduce the risk of recurrent stroke. However, the optimal agent for decreasing LDL-C to lower the risk of recurrent stroke remains unclear. This study aimed to assess the relative effects of various LDL-C -lowering agents for secondary stroke prevention. Methods Several databases were searched from inception up to 2022. Only randomized controlled trials that compared different LDL-C-lowering agents in adult patients with previous strokes were included. The primary endpoint was a recurrent stroke. The surface under the cumulative ranking curve (SUCRA) was also applied to estimate the overall ranking probability of the treatment agents for each outcome. Results Overall, nine trials comprising 17,226 patients were included. Ezetimibe plus statins (RR: 0.56, 95% CrI: 0.35-0.87) and statins alone (RR: 0.90, 95% CrI: 0.81-1.00) reduced the risk of stroke recurrence. Ezetimibe plus statins was superior to statins alone in decreasing the incidence of recurrent stroke (RR: 0.62, 95% CrI: 0.39-0.95). However, treatment with statins was related to an increased risk of hemorrhagic stroke compared to placebo (RR: 1.57, 95% CrI: 1.13-2.21). All agents were related to a decreased incidence of major adverse cardiovascular events. Conclusion Treatment with ezetimibe plus statins was suggested as the most efficacious in decreasing the incidence of recurrent stroke. The analysis also revealed that statin monotherapy was related to an increased risk of hemorrhagic stroke.


INTRODUCTION
Stroke is identified as the second highest cause of death in developed areas and is a significant contributor to permanent disability [1,2].The estimated number of strokes worldwide has doubled in the past two decades [1].The average long-term incidence of stroke recurrence after an initial transient ischemic attack (TIA) or stroke is approximately 10% at one year and increases to 40% at ten years [3].Moreover, patients with previous strokes are at a higher risk of subsequent cardiovascular diseases, such as myocardial infarction (MI), leading to an increased risk of death due to vascular causes [4,5].However, secondary stroke prevention is currently suboptimal, with only 34.4% of stroke patients achieving lipid control targets, according to the EU-ROASPIRE III survey [6].Therefore, there is an urgent need ropean Atherosclerosis Society (EAS) guidelines to decrease the incidence of stroke recurrence in patients with TIA or ischemic stroke [13].However, some concerns exist due to unexpected adverse events.For example, statin therapy may lead to a slight increase in the risk of bleeding events, but the evidence concerning this risk is inconclusive [14][15][16].Moreover, the optimal agent for LDL-C reduction to reduce the incidence of recurrent stroke remains undetermined.
In this study, we used the Bayesian network approach to assess the effects and safety of various LDL-C reduction agents used for secondary stroke prevention.The comparative effects and ranking probabilities of various treatment agents were estimated.Our findings would be helpful for clinicians to guide patient management and for the development of clinical guidelines.

Guidance and Protocol
This work was established according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses for Network Meta-Analyses Extension Statement [17].This study was registered in the OSF portal (https://osf.io/xgpcy)and PROSPERO database (CRD42022333817).

Eligibility Criteria
The studies were screened for eligibility based on their study population (all or a subset of adult patients aged ≥ eighteen years with previous stroke or TIA), interventions, and comparisons (statins vs. placebo, PCSK9 inhibitors with statins vs. statins alone, ezetimibe with statins vs. statins alone), outcomes (primary endpoint of recurrent stroke, secondary endpoints of ischemic stroke, hemorrhagic stroke, major adverse cardiovascular events (MACEs), cardiovascular mortality, and myocardial infarction), follow-up duration (at least one year or 48 weeks), and study design (randomized clinical trials).

Search Strategy
A thorough literature search was conducted in Ovid Med-Line, Ovid EMBASE, and Cochrane CENTRAL from inception to May 19, 2022.Table S1 in the Supplemental materials details the search strategy.In addition, the references of the included trials and relevant reviews on similar topics were searched to identify additional studies.Furthermore, the WHO Clinical Trials Registry Platform and the US National Library of Medicine of Clinical Trials Registry Portal were searched to identify ongoing randomized controlled trials.

Study Selection and Data Extraction
Two authors independently screened the titles and abstracts of all publications after removing duplicates.The fulltext versions of studies were screened when both authors agreed on the study's eligibility.Then the study characteristics of the eligible trials were extracted.Discrepancies were addressed through discussion among the study group.In cases of unclear or missing information, the corresponding author of the relevant study was contacted to request further information.

Quality Assessment
The risk of bias in the included trials was assessed across seven domains using the Cochrane Collaboration Risk of Bias tool [18].Briefly, each study's overall risk of bias was rated as unclear, low, or high.The quality of evidence for each outcome was judged using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) tool [19].The overall quality of evidence for each outcome was rated as high, moderate, low, or very low.

Data Synthesis
The present analysis was conducted using a consistency model to incorporate direct and indirect comparisons, and the method was described elsewhere [20].Briefly, the models were developed based on 40,000 iterations after 15,000 iterations of grinding.We used the ranking functions to rank the intervention level of various treatment agents for each outcome, and the ranking results are presented with the surface under the cumulative ranking curve (SUCRA) values.We analyzed dichotomous variables as risk ratios (RRs) with related 95% credible intervals (CrIs) and continuous variables as the mean differences (MDs) with 95% CrIs.Heterogeneity in the model was assessed using the I 2 test.We assessed publication bias using the Harbord regression test if more than ten trials were synthesized [21].
The present analyses were completed using the relevant packages in R software (version 4.2.1) and Review Manager (version 5.4.0;Cochrane Collaboration).All P values were two-sided, and a value smaller than 0.05 was statistically significant.Analyses for all outcomes were performed for the intention-to-treat (ITT) population.
The details of the eligible randomized controlled trials are shown in Table 1.These trials were published from 1999 to 2020.The number of participants in each trial ranged from 122 to 5,337.The age of the patients ranged from 59 to 68 years.The proportion of females ranged from 25% to 56%.Two trials compared PCSK9 inhibitors with statins to statins alone, one compared ezetimibe with statins to statins alone, and six trials compared statin monotherapy to placebo.
Next, meta-regression analyses were conducted to assess the impacts of the follow-up period, body mass index (BMI), age, and baseline LDL-C level on the risk of stroke recurrence.The results showed an association between increased risk and older age, although this trend did not achieve statistical significance (P: 0.55, Fig. 2).
Subgroup analyses were conducted for patients with ischemic stroke (Table 2).Overall, five trials with 12,511 patients were pooled.The results showed that ezetimibe plus statins (RR: 0.56; 95% CrI: 0.35-0.87;SUCRA: 0.97) was associated with a decreased risk of stroke recurrence.This regimen also ranked first in reducing the incidence of stroke recurrence, followed by PCSK9 inhibitors plus statins (SU-CRA: 0.60) and statins alone (SUCRA: 0.40).

(A higher resolution/colour version of this figure is available in the electronic copy of the article).
stroke.There was a trend toward a reduced risk of hemorrhagic stroke with increasing age.The results also suggested that patients with higher BMI had a higher risk of hemorrhagic stroke, although the trend did not achieve statistical significance (Fig. 4).

Risk of Bias and Quality of Evidence
Figs. (S6 and 7) present the key findings of the risk-ofbias assessments.Four trials were identified to have an overall low risk of bias.The other trials were identified to have an overall high risk of bias.The key findings of the GRADE evaluation of certainty for stroke outcomes are presented in Table S2 (Supplemental material).In general, the quality of evidence for the primary outcome was judged to be moderate to high.

Summary of Findings
In the present study of nine trials with 17,226 participants, we compared the direct and indirect effects of medications on outcomes to provide updated evidence aimed at exploring the optimal agents for preventing stroke recurrence in people with previous strokes.In the present study, several important observations were made.First, ezetimibe plus statins ranked first in reducing the risk of recurrent stroke.Second, statins might increase the risk of hemorrhagic stroke.Third, all three treatment regimens were superior to placebo in decreasing the incidence of MACEs.Furthermore, metaregression analysis suggested a trend toward a higher incidence of hemorrhagic stroke in patients with higher BMI.
Our study revealed that statins might increase the risk of hemorrhagic stroke, which could be explained by the following reasons.On the one hand, lower LDL-C levels may be associated with an increased risk of cerebral hemorrhage.For example, epidemiological studies have shown an association between low LDL-C levels and intracranial hemorrhage [31,32].Some researchers have even recommended avoiding statins in patients with a history of ICH [33,34].Second, in addition to their lipid-lowering effects, statins also have antithrombotic activity, which enhances fibrinolysis and anticoagulation by inhibiting platelet aggregation [35,36].Third, it is also important to note that different classes of statins have different effects on ICH; for example, this study showed that lipophilic statins were likely to increase the risk of hemorrhagic stroke (Fig. S8).Similar findings have been reported in previous studies [37,38].

Comparison with Other Studies
Several meta-analyses have assessed the efficacy of lipid modifying therapies for the primary and secondary prevention of ischemic stroke.One review revealed that PCSK9 inhibitors plus statins and ezetimibe decreased the incidence of ischemic stroke without increasing the incidence of hemorrhagic stroke [39].Another systematic review showed that statins increased the risk of hemorrhagic stroke (RR: 1.15, 95% CI: 1.00-1.32),but PCSK9 inhibitors did not increase the risk (RR: 0.93, 95% CI: 0.58-1.51)[40].Only one network meta-analysis assessed different statin types for the secondary prevention of stroke [41].Evidence from this study indicated that patients treated with statins had an elevated risk of hemorrhagic stroke (0.6%) compared to those treated with placebo/no statins.In particular, the administra-tion of 80 mg atorvastatin per day or 40 mg simvastatin per day should prompt careful consideration of the potential risk of hemorrhagic stroke.Previous studies on this topic have yielded similar results [42,43].

Study Strengths and Limitations
To date, this study is the most extensive systematic review and the only network meta-analysis to examine the efficacy and safety of different LDL-C-lowering therapies for the secondary prevention of stroke.The large sample size of the present study gave credibility to our results because of the improved precision of estimation regarding the treatment effects.It allowed informed suggestions for choosing optimal treatment agents.In addition, we conducted subgroup analysis for selected patients with ischemic stroke and ranked the quality of evidence for stroke outcomes according to the GRADE method.Moreover, meta-regression analyses were conducted to test the effects of different variables on the risk of stroke recurrence and hemorrhagic stroke, which was helpful for future research.
There are a few limitations of this study that need to be discussed.First, participants and care providers were aware of the treatment allocation in some trials, resulting in an increased likelihood of bias regarding the assessment of outcomes in the absence of blinding.Second, we focused on long-term outcomes and included studies with a follow-up duration of at least one year of follow-up.Because the follow-up period varied across trials, we performed a metaregression analysis to explore whether the follow-up duration influenced the effects of LDL-C-lowering therapies but did not observe any such relationship (P: 0.449).Third, most of the included trials did not provide data on LDL-C reduction; therefore, we were unable to assess the comparative effects of different treatment regimens (Fig. S9).

Study Implications
The ACC/AHA and ESC/EAS guidelines recommend intensive lipid-lowering therapy in persons with previous TIA or ischemic stroke [13,44,45].However, the optimal type of LDL-C lowering agent has not been specified.Based on the moderate quality of evidence, we suggest that ezetimibe with statins might be more effective than monotherapy with statins in preventing stroke recurrence.Our analyses also suggest that a regimen of PCSK9 inhibitors with statins is likely preferable to statins alone to reduce the incidences of MACEs and MI.However, it is suggested that treatment with statins alone is associated with an increased incidence of hemorrhagic stroke.Clinicians should comprehensively evaluate drug efficacy, safety, and costeffectiveness when choosing a specific agent.

CONCLUSION
This network meta-analysis indicated that ezetimibe plus statins might be the most effective regimen for decreasing the incidence of recurrent stroke in people with previous stroke.Although statins have shown a superior effect in decreasing the incidence of recurrent stroke compared to placebo, attention should be given to the potential increased risk of hemorrhagic stroke that they may cause.Regarding cardiovascular events, although all the agents decreased the risk of major adverse cardiovascular events and myocardial infarction, PCSK9 inhibitors were found to be the most effective treatment agent compared with either placebo or statins.These findings provide novel and essential evidence for clinicians to guide therapeutic strategies.

AUTHORS' CONTRIBUTIONS
XW and LM designed the meta-analysis, XW and CY searched for relevant studies, XW and YQC selected the studies, extracted the relevant information, XW and DKW synthesized the data, and XW wrote the first draft of the paper.All authors revised the manuscript and approved the final manuscript as submitted, and agreed to be accountable for all aspects of the work.

STANDARDS OF REPORTING
PRISMA guidelines and methodology were followed.

Fig. ( 1
Fig. (1).Summary of the recurrent stroke outcome.(A) Network plot of recurrent stroke.The width of the lines is proportional to the number of studies comparing every pair of treatments, and the size of each circle is proportional to the number of participants.(B) The forest plot shows the risk ratio (RR) and credible interval (CrI).(C) Ranking probability graph of each treatment agent.The SUCRA values for each treatment were as follows: 60% for PCSK9 inhibitor plus statins, 97% for ezetimibe plus statins, and 40% for statins alone.SUCRA: surface under the cumulative ranking curve.(A higher resolution/colour version of this figure is available in the electronic copy of the article).

Fig. ( 2 )
Fig. (2).Meta-regression analysis for the interaction of (A) age, (B) BMI, (C) baseline LDL-C level, and (D) follow-up period on the risk of recurrent stroke.BMI: body mass index; LDL-C: low-density lipoprotein cholesterol.(A higher resolution/colour version of this figure is available in the electronic copy of the article).

Fig. ( 3 ).
Fig. (3).Network analysis for ischemic stroke and hemorrhagic stroke.(A) The forest plot for ischemic stroke.(B) The SUCRA value of each treatment for ischemic stroke.(C) The forest plot for hemorrhagic stroke.(D) The SUCRA value of each treatment for hemorrhagic stroke.CrI: credible interval.SUCRA: surface under the cumulative ranking curve.(A higher resolution/colour version of this figure is available in the electronic copy of the article).

Fig. ( 4 )
Fig. (4).Meta-regression analysis for the interaction of (A) age, (B) BMI, (C) baseline LDL-C level, and (D) follow-up period on the risk of hemorrhagic stroke.BMI: body mass index; LDL-C: low-density lipoprotein cholesterol.(A higher resolution/colour version of this figure is available in the electronic copy of the article).

Fig. ( 5 ).
Fig. (5).Network analysis for other outcomes.(A) The forest plot for MACE.(B) The SUCRA value of each treatment for MACE.(C) The forest plot for cardiovascular mortality.(D) The SUCRA value of each treatment for cardiovascular mortality.(E) The forest plot for myocardial infarction.(F) The SUCRA value of each treatment for myocardial infarction.MACE: major adverse cardiovascular event.CrI: credible interval.SUCRA: surface under the cumulative ranking curve.(A higher resolution/colour version of this figure is available in the electronic copy of the article).

Table 1 . Characteristics of studies included in the systematic review.
Abbreviations: NA: not available; BMI: body-mass index; LDL-C: low-density lipoprotein cholesterol; TIA: transient ischemic attack.